1. Field of the Invention
The present invention relates to a composite sheet material that exhibits low emittance characteristics at both of its outer surfaces for limiting radiant heat transmission therethrough. This sheet material may be used with particular advantage as one component of an insulating shade device described and claimed in U.S. Pat. No. 4,039,019 (Hopper). However, this sheet material may also be used in any other application in which a light weight, low mass sheet material is desired to minimize radiant heat transmission from one area to another.
2. Description of the Prior Art
Various film or sheet materials that inherently exhibit certain low emittance characteristics have been proposed in the past. For example, U.S. Pat. No. 3,775,226 (Windorf) discloses a solar control film that is a composite material of two outer polyester layers with an adhesive and a vacuum deposited aluminum metal layer interposed between them. The sheet material is attached by suitable means to a window and allegedly reduces the transmission of infrared, visible, and ultraviolet radiation from the sun through the window. U.S. Pat. No. 3,899,621 (Willdorf) discloses a similar sheet material that incorporates intermediate layers of polyurethane utilized as bonding strata. However, in each of the Windorf and Willdorf patents, polyester material comprises an outer coating to a metalized layer.
U.S. Pat. No. 3,565,752 (Grossman) discloses a material that incorporates a cryogenic adhesive joint and comprises aluminumized polyester films bonded with alkyl acrylate adhesive. The two metal layers are bounded by the two polyester layers and are joined together with the adhesive.
U.S. Pat. No. 3,516,720 (Mauer) discloses a thin film for coating sunglasses that incorporates a metal foil sandwiched between two layers of transparent material. U.S. Pat. No. 3,682,528 (Apfel et al.) discloses an infrared interference filter having a glass substrate, a precoat layer, a silver layer, a dielectric layer, another silver layer and another dielectric layer.
The materials described and illustrated in the prior art patents noted above are characterized by certain drawbacks.